Daniel Day-Lewis smoking in Nine, among the films subsidised by government tax credits. Photograph: Allstar

Health experts have accused the government of spending more on subsidising American films that contain smoking scenes than on anti-tobacco campaigns.

Researchers at Imperial College London calculated that between 2003 and 2009, £338m of tax credits in Britain went to US-produced films with imagery "promoting" tobacco use.

Foreign film-makers receive 16% tax relief against their British production costs if more than a quarter of their budget is spent in Britain. More than three-quarters of British film subsidies go to US production companies.

"In the period we looked at, the government gave £48m a year in tax credits to American films that feature smoking, almost all of which were rated suitable for children and adolescents," said Christopher Millett, from the School of Public Health at Imperial College London. "By comparison, the government spent £23m a year on mass media anti-smoking campaigns."

Research has shown that young people heavily exposed to tobacco imagery in films are more likely to begin smoking than those who are only lightly exposed. This led the World Health Organisation (WHO) to recommend in 2009 that films with scenes of smoking should be given an adult content rating, creating an economic incentive for producers to leave smoking out of their films.

But in the open access journal PLoS Medicine, the Imperial team says its findings show the recommendation has been largely ignored in the UK, US and Canada. They accuse all three governments of underwriting many films that promote youth smoking with public subsidies.

They estimate that of the "high-grossing" films that had their tobacco content monitored, 66% featured tobacco imagery. More than half (57%) containing scenes of smoking were rated U, PG or 12A, and only 8% were given an 18 certificate.

Millett said that by "promoting smoking in films" the government was "seriously undermining" tobacco control efforts. "We think film subsidy programmes should be harmonised with public health goals by making films with tobacco imagery ineligible for public subsidies," Millett said. "This wouldn't cost anything to implement so in the current financial climate it should be an attractive policy option."

His comments were echoed by Martin Dockrell, director of research at Action on Smoking and Health. "The research is clear: the more a young person sees smoking in films the more likely they are to try smoking themselves," he said.

"This study reveals the astonishing fact that the government has spent an average of almost £50m a year subsidising films that encourage children to smoke, more than twice as much as they spent on advertising supporting people to quit."

The previous Labour government published a tobacco control strategy that recommended smoking "must not be condoned, encouraged or glamorised in other programmes likely to be widely seen or heard by under-18s unless there is editorial justification".

But health campaigners attacked the recommendations for being too vague and falling significantly short of actions proposed by the WHO.

"This year the government promised to look at what more could be done to tackle the role of TV and films in stimulating smoking among children," Dockrell said. "At the moment we have a film funding system that makes the problem worse., by investing millions in films made for young people that have the effect of encouraging them to smoke."